1. Field of the Invention
This invention relates to compounds which release a silver halide solvent in the presence of alkali and to photographic products and processes employing said compounds.
2. Description of the Prior Art
In various photographic processes for forming images in either black-and-white or in color, it is often desirable to include one or more of the photographic reagents in the photographic film unit. In many instances, the photographic reagent may be contained initially in either the processing composition or in the film unit, the latter being preferred to reduce the number of ingredients in the processing composition. In other instances, the particular photographic reagent selected may not be sufficiently stable in alkali to provide the requisite shelf life of the processing composition, or it may be incompatible, e.g., reactable with another ingredient in the processing composition. In still other instances, it may be desirable to provide a given reagent at some particular time during the development process which requires positioning of the reagent in a particular layer or layers of the film unit. In all of these instances it is desirable that the reagent initially positioned in the film unit be stable, i.e., substantially inert until it is required during the development process.
One class of compounds which releases a photographic reagent during processing in the presence of alkali is disclosed in U.S. Pat. No. 3,698,898 of J. Michael Grasshoff and Lloyd D. Taylor. These compounds are phenols and naphthols (including protected derivatives thereof) containing a photographic reagent bonded to a nuclear carbon atom through a methylene substituent in a position ortho or para to the hydroxyl group. The photographic reagent released may be an antifoggant, development arrester or restrainer, toning agent, silver halide solvent, etc. U.S. Pat. No. 3,932,480, a continuation-in-part of Ser. No. 230,064 filed Feb. 28, 1972, now abandoned, which, in turn, is a division of aforementioned U.S. Pat. No. 3,698,898 is directed to such compounds which release a thiosulfate silver halide solvent.
Another class of compounds that release a silver halide solvent in alkaline solution during processing is disclosed and claimed in copending U.S. Patent Application Ser. No. 294,311 of Alan L. Borror and Ernest W. Ellis filed Aug. 19, 1981. These compounds release a silver halide solvent via a Michael addition of hydroxide followed by a retro-aldol reaction and include compounds, such as, ##STR2## wherein R.sup.1 and R.sup.2 are groups selected to provide a given release rate at a given alkali concentration.
The present invention is concerned with a new class of compounds that release a silver halide solvent in the presence of alkali.